Since their invention by IBM in 1956, hard disc drives (HDDs) have dramatically decreased in size, cost, data access time, and power consumption, and have even more dramatically increased in data storage capacity. At the time of filing this application, 1 TB to 4 TB HDDs are common for desktop computing applications. Indeed, the smallest data storage capacity HDD commonly available is 320 GB.
A consequence of the rapid increase in drive capacities over a brief time span is that many legacy computing and communication systems in use were designed for—and indeed require—HDDs of far lower data storage capacity. For example, the BIOS system in some computer motherboards, and some older operating systems (e.g., Windows® 2000), do not recognize HDDs larger than 128 GB.
Other systems, such as Point of Sale (POS) terminals, were designed to operate with, e.g., 40 GB HDDs. In many cases, a single, optimized disc image—that is, the collection of data resident on a full HDD—is created, and replicated across the HDDs in all POSs in an enterprise. When a HDD fails, or a new, compatible POS is added to the system, the hard disc image cannot be loaded, as new 40 GB drives are simply not manufactured. Hard disc imaging software cannot load a smaller (e.g., 40 GB) disc image onto a larger (e.g., 320 GB) HDD, due to the size mismatch.
Clipping is a process by which a larger data capacity HDD is made to emulate a smaller capacity HDD. Only a portion of the data storage space on the larger HDD is allocated for use, or made available for read and write operations, and only this portion is reported by the HDD. In this manner, a device driver, BIOS, operating system, or other software attempting to access the HDD “sees” the lower data capacity HDD, and can function properly. The excess data storage space is simply never accessed or utilized.
HDD clipping is implemented in firmware in the control electronics of a HDD. In the case of a wide-spread need, such as emulating a 128 GB drive for compatibility with widely deployed legacy operating systems, an entire line of HDDs includes the clipping functionality, which may be optionally invoked by setting jumpers on the drive. In the case of special requirements, such as providing 40 GB clipped drives for POS terminals, the appropriate firmware may be included as a custom option from the HDD manufacturer.
HDD clipping is typically implemented by simply mapping the entire (lower capacity) disc image size to continuous sectors along one track, or across a few adjacent tracks, of one or more HDD platters. This minimizes the firmware complexity of translating track and sector specifiers, and additionally provides the lowest data latency, as the actuator arm that positions the read/write head may not need to move at all, and if so it only moves to adjacent or very nearby tracks.
HDDs, however, are designed to move the actuator arm to position the read/write head over all tracks on the platter(s). Additionally, HDDs are designed to move the read/write head to a “landing” area—referred to as unloading the head—prior to powering down the HDD. In implementations where HDDs are run extensively without powering down, such as POS terminals that are never turned off, the actuator arm does not unload the head by moving it to the landing zone. This may cause a failure due to migration of lubricant in the mechanical couplings of the actuator mechanism. The lube migration—normally prevented by routinely-occurring load/unload cycles—may prevent the HDD from unloading the read/write head when a power-down is eventually attempted. This has been known to occur in as little as two weeks of continuous operation, even with the actuator arm otherwise moving over all tracks of the platter.
This problem of restricted freedom of motion due to failure to fully exercise the actuator arm is exacerbated in a clipped drive, in which the actuator arm moves over only, at most, a few tracks when reading or writing data. In this case, the actuator arm does not move over all the data areas of the platter, much less to the landing zone. This can accentuate the migration of lubricant to impede such motion if it is ever required (e.g., upon a power-down operation).
One approach to prevent clipped HDD failure due to severely limited range of motion of the actuator arm is to periodically “exercise” the actuator arm by driving the read/write head to various tracks on the platter, as well as unloading the heads on the landing zone, and loading them onto the platter. One known HDD exercise program, recommended to be run prior to a system shutdown or restart, performs 40,000 seeks, with a load/unload operation every 1,000 seeks. This provides 40,000 full-stroke seek pairs 40 loads/unloads. This HDD exercise is sufficient to disperse any lubricant build-up in areas in which mechanical parts of the actuator need to move. However, periodic use of a HDD exercise program renders the drive unusable for the duration of the exercise, which will cause performance degradation if the system attempts to read or write the clipped HDD at the same time.
The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.